New developments in neonatal technology have resulted in the survival of smaller infants who have limited retinal vascular development at birth and, thus, greater susceptibility to retinopathy of prematurity (ROP). It is reasoned that as more and smaller premature babies survive, the incidence of visual loss from ROP will continue to increase unless effective treatments are found. Advanced ROP is characterized by a period of unregulated growth of retinal blood vessels. This growth occurs by a process known as angiogenesis, indicating that the new vessels form by an abnormal sprouting of exiting vessels. The loss of vision from angiogenesis is not unique to ROP; collectively, ocular disorders with this feature constitute the leading cause of blindness in the U.S. The significance of research aimed at understanding retinal angiogenesis in an animal model of one of these diseases is amplified by the potential of applying the new knowledge to other ocular conditions in which angiogenesis plays a role. The ultimate goal of this project is to develop methods to prevent retinal angiogenesis based upon understanding gained from studies of relevant models. We propose to use pure cultures of retinal microvascular endothelial cells (RMEC), a well- established rat model of ROP and a mouse model of ROP currently under refinement. With these tools, we will address the following four interrelated aims: 1) investigation of the role of a pivotal tyrosine kinase, Src, in RMEC proliferation and tube formation and in ROP-related retinal angiogenesis; 2) characterization of the proteolytic aspect of ROP-related retinal angiogenesis, emphasizing PAI-1, MMP-2 and -9 and TIMP-2; 3) characterization of the roles of angiopoietins 1 and 2 in retinal vasculogenesis and angiogenesis; and identification of factors responsible for the angiostatic effect of penetrating ocular injury.